An ultrastructural and biochemical comparison of erythrocyte membranes from normal RBCs and sickled RBCs is being conducted. Using cationized ferritin as a membrane probe we have found that the irreversibly sickled cells (ISCs) have 10% fewer anionic sites on their surface than do normal cells. This finding probably explains why ISCs have a shorter life span than normal cells because RBCs with a reduced negative charge are preferentially phagocytized by macrophages. Use of concanavalin A (Con A) as a probe has revealed no difference in the distribution of binding sites on ISCs and normal cells. Freeze-cleave studies also reveal no difference in the intramembranous particle (IMP) distribution between normal and ISCs. Pronase treatment followed by incubation in Con A causes both the Con A sites and the IMPs to cluster as a result of a transmembrane effect in which spectrin becomes aggregated. Thus, agents acting only on the outer surface of the membrane can alter the inner, cytoplasmic face of the membrane. Two-dimensional gel electrophoresis has revealed over 200 polypeptides in the erythrocyte membranes. Comparisons are currently being made between normal and ISC membranes. In addition, a few patients appear to have a consistent altered protein pattern and we are currently determining if this correlates with a clinical history of numerous painful crises.